Key Chemical Properties and Uses of Ammonium Dichromate
How Do You Define The Terminology Ammonium Dichromate(NH4)2Cr2O7?
Ammonium dichromate is an inorganic compound with the chemical formula (NH4)2Cr2O7. It is orange-red needles produced during crystallization.
Ammonium dichromate is a salt consisting of ammonium ions and dichromate ions, a toxic chemical salt used to sensitize organic emulsion. It is more sensitive to light. It is readily ignited and burns to leave a sizable green residue. If ammonium dichromate is heated in a closed container, it may rupture due to the decomposition of the material. It also acts as a reliable oxidizing agent mixed with or contaminated with combustible material.
The following figure highlights a few of the things about Ammonium dichromate:
Because of its application in demonstrations of tabletop "volcanoes", Ammonium dichromate is sometimes also termed as Vesuvian Fire. However, in schools, this demonstration became unpopular due to the compound's carcinogenic nature. It has also been used in pyrotechnics and the early days of photography.
A glimpse, let's have a look to the names of Ammonium dichromate:
IUPAC name – diammonium oxido-(oxido-dioxo-chromio) oxy-dioxo-chromium,
Other names – Ammonium bichromate
Ammonium pyrochromate, Chromic acid, diammonium salt; diammonium dichromate; Ammonium bichromate; Ammonium pyrochromate.
The following points and table give a depth-understanding of the various features or characteristics of Ammonium dichromate. These are as follows:
The density of ammonium dichromate is 2.12g/cm 3
It has a melting point of 180°c
Exact molecular mass - 251.924166
Ammonium dichromate is an explosive compound.
The action makes chromic acid on ammonium hydroxide with subsequent crystallization.
Features of Ammonium Dichromate
Ammonium Dichromate Structure – (NH4)2Cr2O7.
The Ammonium dichromate follows a particular pattern or structure. This can be seen as follows:
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Properties of Ammonium Dichromate
The properties of Ammonium dichromate are explained by dividing them into two main categories. These are:
Physical Properties.
Chemical Properties.
These will be explained one by one as follows:
Physical Properties of Ammonium Dichromate – (NH4)2Cr2O7
The physical properties of Ammonium dichromate are as follows:
It is orange-red crystals.
It is soluble in water and alcohol at room temperature.
Ammonium dichromate is odorless.
Other Properties Can Be Made More Transparent With The Help of The Following Chart
Chemical properties of Ammonium Dichromate-
At room temperature and pressure, it is orange, acidic crystal soluble in water and alcohol. On heating Ammonium dichromate, it undergoes decomposition, resulting in chromium (III) oxide and nitrogen gas formation.
(NH4)2Cr2O7(s) → Cr2O3(s) + N2 (g) + 4H2O (g).
Hazards and safety of Ammonium Dichromate -
Main hazards of ammonium dichromate are as follows:
Dangerous, very toxic, a carcinogen, mutagen, oxidizing, dangerous for the environment.
To deal with these hazards, one needs to follow safety measures. These includes:
Safety: Ammonium dichromate, like all chromium (VI) compounds, is highly toxic and is also explosive under certain conditions. It is also a strong irritant.
Safety measures need to be taken while using ammonium dichromate. Wear eye protection and avoid skin contact with ammonium dichromate (wear gloves).
Uses of Ammonium Dichromate – (NH4)2Cr2O7
Ammonium dichromate has various applications. These are explained as follows:
Ammonium dichromate is used in sensitizing solutions used in lithography.
They are used in pyrotechnics, lithography, and photoengraving. It is also used as a magnetic recording material.
It is used as an approved pesticide and used as a mordant for dyeing, used as a pigment.
It is also used as a mordant for dyeing pigments, in the manufacturing of alizarin, chrome alum, leather tanning, and oil purification.
Reactions: Ammonium dichromate depicts various reactions, and these include:
Oxidation Reactions
Ammonium dichromate acts as an oxidizing agent. Often reacts violently with any reducing agent: the more influential the reducing agent, the more violent the reaction. Even in the oxidation of aliphatic alcohols, the compound is being applied. This is being used for their corresponding aldehydes and ketones in ZrCl4/wet SiO2 in solvent-free conditions. This is done again with relatively high yields.
Reactions: Consisting of tabletop volcanoes and thermal decomposition.
If you add a few drops of ethanol to a small pile of ammonium dichromate and ignite, you will notice a spark will emit, and an ash-like product will form. This phenomenon resembles the eruption of a volcano.
FAQs on Ammonium Dichromate: Structure, Properties, and Applications
1. What is ammonium dichromate and what is its chemical formula?
Ammonium dichromate is an inorganic compound and a strong oxidising agent. It consists of ammonium cations and dichromate anions. At room temperature, it exists as an orange-red crystalline solid. Its chemical formula is (NH₄)₂Cr₂O₇.
2. How is the structure of ammonium dichromate organised in terms of its chemical bonds?
The structure of ammonium dichromate is primarily ionic. It is formed by the electrostatic attraction between two ammonium cations (NH₄⁺) and one dichromate anion (Cr₂O₇²⁻). However, within these polyatomic ions, the bonds are covalent. The nitrogen and hydrogen atoms in the ammonium ion are covalently bonded, as are the chromium and oxygen atoms in the dichromate anion.
3. What are the key physical and chemical properties of ammonium dichromate?
The key properties of ammonium dichromate are:
Appearance: It is a bright, orange-red crystalline solid.
Solubility: It is soluble in water and ethanol.
Oxidising Nature: It is a powerful oxidising agent due to the chromium(VI) in the dichromate ion.
Thermal Decomposition: When heated, it undergoes a dramatic decomposition reaction, often called the 'Ammonium Dichromate Volcano'.
Molar Mass: Its molar mass is approximately 252.07 g/mol.
4. What happens when ammonium dichromate is heated, and why is this reaction called the 'volcano experiment'?
When ammonium dichromate is heated, it undergoes exothermic thermal decomposition, producing solid green chromium(III) oxide (Cr₂O₃), nitrogen gas (N₂), and water vapour (H₂O). The balanced chemical equation is:
(NH₄)₂Cr₂O₇(s) → Cr₂O₃(s) + N₂(g) + 4H₂O(g)
This reaction is famously known as the 'volcano experiment' because the orange-red crystals ignite and erupt, throwing out a large volume of fluffy, green chromium(III) oxide powder that resembles volcanic ash.
5. Why is an aqueous solution of ammonium dichromate acidic?
An aqueous solution of ammonium dichromate is acidic due to salt hydrolysis. The compound is a salt formed from a weak base (ammonium hydroxide, NH₄OH) and a relatively strong acid (dichromic acid, H₂Cr₂O₇). In water, the ammonium ion (NH₄⁺) reacts with water to produce hydronium ions (H₃O⁺) and ammonia (NH₃), which increases the concentration of H⁺ ions in the solution, making it acidic.
6. What are some important real-world applications of ammonium dichromate?
Ammonium dichromate has several important applications, including:
Pyrotechnics: It is used in fireworks and in the 'volcano experiment' demonstration.
Photography: Historically used in early photography and lithography as a photosensitizer.
Catalysis: It acts as a catalyst for certain chemical reactions.
Dyeing: Used as a mordant to fix pigments onto fabrics in the textile industry.
Laboratory Use: It serves as a source for producing pure nitrogen gas in a laboratory setting.
7. What is the main difference between ammonium dichromate and ammonium chromate?
The main differences lie in their anion and colour:
Anion and Formula: Ammonium dichromate contains the dichromate anion (Cr₂O₇²⁻) and has the formula (NH₄)₂Cr₂O₇. Ammonium chromate contains the chromate anion (CrO₄²⁻) and has the formula (NH₄)₂CrO₄.
Colour: Ammonium dichromate is an orange-red solid, while ammonium chromate is a yellow solid.
8. What are the key safety precautions to follow when handling ammonium dichromate?
Ammonium dichromate is hazardous and must be handled with care. Key safety precautions include:
Wear appropriate personal protective equipment (PPE) such as gloves and safety goggles.
Handle it in a well-ventilated area or under a fume hood to avoid inhaling dust.
Keep it away from flammable materials as it is a strong oxidiser and can cause fires.
Store it in a cool, dry place away from heat sources to prevent accidental decomposition.
